This invention relates to an apparatus and method for detecting .alpha.-rays present in a specified energy range, which may be emitted from particles dispersed in a gas, and more particularly, particles emitted by an aerosol.
Systems used to detect the energy of .alpha.-particles permit the detection of .alpha.-rays which are emitted by artificially produced nuclides. The energy level of .alpha.-rays emanating from artificially produced nuclides frequently is approximately the same as the energy level of .alpha.-rays emitted from naturally occurring .alpha.-emitters, such as disintegration products of radon or thoron.
Prior art systems developed to perform this function utilize a chamber having a measuring space therein through which the gas is directed. The measuring space is defined by a first boundary wall consisting of the receiving surface of a filter, and a second boundary wall which is opposite the first boundary wall and which consists of the receiving surface of an .alpha.-ray detector. The filter separates the particles from the gas. The .alpha.-ray detector is an energy-discriminating .alpha.-ray detector which measures and indicates the energy of the separated .alpha.-particles.
The prior art systems referred to, however, suffer from a distinct disadvantage. As the .alpha.-rays travel from the receiving surface of the filter to the receiving surface of the detector, they lose energy due to the presence of air in the measuring space. The statistical effect of energy loss as the .alpha.-particles travel between the receiving surfaces results in the detection of .alpha.-particles which have energy levels different from their original energy levels. This effect causes overlapping of the measured energy ranges, reducing significantly the ability of the .alpha.-detector to discriminate between originally-differing .alpha.-ray energies.